This invention relates generally to firearms barrels. More particularly, this invention relates to firearms barrel cartridge chambers embodying release grooves.
The pressure developed within the cartridge case on firing a bullet tends to deform the case and press it tightly against the inner wall of the cartridge chamber. Consequently, friction between the cartridge case and cartridge chamber may become so great that extraction of the case becomes extremely difficult.
It has long been recognized in the art that equalizing the pressure across the case will reduce case deformation and improve case extraction. Typically, longitudinal grooves are formed in the cartridge chamber wall to equalize the pressure. It is desired that the grooves have an accurate width and depth, that they commence at an exactly defined point at the forward end of the cartridge chamber and follow the tapered rearward enlargement of the cartridge chamber. Such conventional grooved structures have proved effective in facilitating case extraction but are extremely difficult to produce.
A number of cartridge chamber designs and methods for forming cartridge chambers have been advanced. For example, Koch U.S. Pat. No. 3,736,693 discloses a cartridge chamber having a polygonal cross-section that merges into a circular profile near the outer end of the cartridge chamber. The corners of the polygonal cross-section are rounded to form the release grooves.
Seifried U.S. Pat. No. 3,943,821 discloses a tubular member threadably mounted within a barrel. The tubular member has balance grooves which exceed the number of grooves in the bullet chamber of the barrel. Due to the increased number of gas pressure balance grooves within the powder portion of the cartridge chamber, the surface area which supports the cartridge is reduced. The slide resistance of the cartridge is thereby substantially decreased. The grooves extend from a cylindrical annular groove formed between the tubular member and the inner end of the barrel to a point forward of the tubular member rear face.
Lee U.S. Pat. No. 2,464,323 discloses a punch which is employed for fluting gun barrel chambers.